1. Field of the Invention
This invention relates to continuous wave adaptive signal processing systems and more particularly, relates to a spread spectrum carrier wave altimeter.
2. Description of the Prior Art
Radio frequency altimeters are known. The most common type of radio frequency altimeter transmits a burst of energy from a transmitting antenna and receives the reflected energy signal back at a receiving antenna. A ranging system is employed to determine the time required for the signal to make the round trip which is converted by known techniques into distance or elevation.
Continuous wave (CW) radio frequency altimeters are known, but heretofore have had limited use because the system is generally limited to a range of no more than ten thousand feet. The main reason that CW altimeters have limited use is that the signal produced at the transmitting antenna is coupled by leakage paths into the receiving antenna and the receiving signal processing path. When the leakage signal becomes much stronger than the desired signal, produced by reflection from a distant object, the leakage signal masks the desired signal and cannot be properly recovered. Ways have been suggested to extend the range of a CW altimeter but heretofore have been expensive and/or lacking in performance.
A radar altimeter is only one type of receiving and transmitting system which suffers from the above-mentioned leakage problem. Any continuous wave radio frequency communications system, which requires that the transmitting path be close to the receiving path will have replicas of the transmitted signal inherently coupled into the receiving path. Jamming systems, which generate jamming signals and also attempt to monitor the signal being jammed in order to measure the effectiveness of jamming, are plagued with the same problem when the receiving monitor system is placed in close proximity to the jamming transmitter.
A radio frequency altimeter, which generates bursts of energy, are easy to detect and are not suitable for use in a covert vehicle such as bombers and cruise missiles.
There is a need for an integral continuous wave transmitting and receiving system which is not affected by leakage signals. It would be desirable that such a system would be capable of use in a covert continuous wave radar altimeter as well as less sophisticated integral systems.